


Betrothal

by Bookkbaby



Category: Supernatural
Genre: M/M, mermaid au
Language: English
Status: Completed
Published: 2014-07-06
Updated: 2014-07-06
Packaged: 2018-02-07 16:06:14
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 4,120
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/1905258
Author URL: https://archiveofourown.org/users/Bookkbaby/pseuds/Bookkbaby
Summary: <blockquote class="userstuff">
              <p>Castiel has a gift to give to Dean.</p>
            </blockquote>





	Betrothal

**Author's Note:**

> Art is NOT MINE. It is the work of the amazing gabrielmanga, who kindly allowed me repost the image along with the fic I wrote for it. You can find the original post here: http://gabrielmanga.tumblr.com/post/19274390553/dinaga-wanted-a-mermaid-castiel-then-she-shall
> 
> Wrote this back when I was just getting into the fandom, in March 2012!

Castiel's fins fluttered nervously, sunlight reflecting off of his scales as he flexed his tail. In his hand, he held a perfectly white pearl the size of a tiger shark's eye. It had taken him months to find just the right gift and he had discarded numerous other pearls of less brilliant color and smaller size.  
  
His tail twitched again with nerves and his fingers tightened around the precious stone. Now all that remained was to see if Dean would accept it.  
  
Cas looked up towards the ocean's surface. The sun was high in the sky, but not perfectly over the small stretch of reef Dean and Cas had claimed as their meeting grounds. The reef was shallow enough that Dean could dive it safely but deep enough that Cas didn't get dizzy from the lack of pressure. Cas had swum over early, hoping to avoid at least some of Gabriel's teasing on how his 'little bro was finally gonna pop the question'. Still, now that he was waiting here with only the sound of the current for company, Cas almost wished he hadn't been in such a rush. The near-silence was much more nerve-wrecking than any of Gabriel's taunts.  
  
A shadow suddenly fell over him and Cas looked quickly towards the source. His eyes found the hull of Dean's boat and he relaxed, waiting expectantly for the human to enter the water as he chastised himself for being so distracted he hadn't even heard the small boat's motor. There was the usual great splash as the anchor came down, headed unerringly for an empty stretch of sand at the edge of the reef. Minutes later, there was a second splash as Dean jumped in.  
  
Dean glanced around briefly, his eyes almost immediately landing on Cas. Dean smiled, the expression accomplished by minimum facial movements and lots of brightness in his eyes. Castiel smiled back, the minuteness of his expression from nerves rather than necessity. Dean's eyes flickered with concern for a moment and then he turned his attention to the rope connecting the anchor to the boat and began descending. His descent was methodical and he stopped every few feet to adjust to the pressure, just as his father had taught him. Finally, after an excruciating wait, Dean was finally low enough to swim over to Castiel. His strong arms propelled him through the water quickly, the weight belt and the tank on his back fighting his natural buoyancy to keep him under the waves. As always, he wore dark green swimming trunks instead of a wetsuit.  
  
Cas clutched the pearl to his chest and reached for Dean with his other hand. Dean grabbed his hand and used that to pull himself the rest of the way in. Their fingers twined together automatically, like they had a thousand times before, and then Dean was in Castiel's personal space and grinning down at the merman. The small amount of magic Cas had was enough to protect Dean while they were in contact, enough to keep his mask free from saltwater and carry their voices clearly to one another. Gabriel had more control over the ocean's energy and could probably create a bubble of air for Dean beneath the waves, one sturdy enough that Dean wouldn't need his air tank, but Castiel was not his brother's equal. The most he could manage was coaxing the currents to carry sound between them and to stay out of Dean's mask no matter what expression Dean made. When not touching Castiel, the slightest grin could crack the mask's seal and saltwater would pour in.  
  
"Hey," Dean said, resting his other hand on Castiel's shoulder. Castiel's tail kept them steady with slow, lazy flicks. The merman usually took on the task of keeping them steady in the water, since he was stronger than Dean and able to tread water as naturally as a human stood still. "Miss me?" It had been three days since Dean's last visit. Though he tried to visit often, there was still a limit to how frequently a human could dive without developing what Dean called 'the bends'. Dean had been stricken with it last year after diving too deeply too frequently in order to visit Castiel and John Winchester, Sam, and Cas had all put their feet (or fins) down and limited the time Dean could spend under the sea. Much as Castiel missed Dean while he was away, nothing was worth seeing Dean sluggish and unresponsive in the water. It had been frightening enough the first time Cas had seen it, back when Dean had just been a little boy who had swum away from his father and brother before his regulator malfunctioned. The second time, after Dean had become someone Castiel cared about, it had been unbearable.  
  
Castiel's hand tightened around Dean's. Human bodies were terrifyingly fragile.  
  
"Cas? You with me, buddy?" Dean asked, trying to catch Castiel's gaze. Cas jerked himself out of the memories and offered the human a reassuring smile.  
  
"Yes, I did miss you," he said. "I always do."  
  
Dean chuckled and shifted closer, touching their foreheads together.  
  
"You giant girl," he teased. "Next you'll be bringing me seaflowers or something and writing me poetry."  
  
Cas frowned.  
  
"Would you like a bouquet of seaweed?"  
  
Dean laughed at that and shook his head. His hair, though short, kept waving a few seconds after he stopped shaking his head.  
  
"No." Dean glanced towards the pearl wrapped in Castiel's fist. "What do you have there?"  
  
Castiel's fingers flexed around the gem. If Dean thought Cas admitting that he had missed the human was feminine, something Dean seemed to avoid at all costs, would a pearl truly be the proper betrothal gift? It was traditional, but perhaps Dean would have preferred the jaws and skin of a great white shark. While Cas wasn't the village's most skilled hunter - that distinction belonged to Uriel - he was still top-rate.  
  
"It's... it's nothing, I-" Cas started to say, but Dean was already reaching for the pearl. With a quiet sigh, knowing he was stronger than Dean but unable to deny him, Cas opened his hand and offered it to Dean for inspection. His heart hammered in his chest as Dean picked it up and studied it from all sides. The human let out a low whistle.  
  
"Damn, this is amazing. Where'd you find this?" he asked. Castiel looked off into the distance, well beyond the far edge of the reef, fins and arms shaking.   
  
"It's yours, if you want it," Cas said. Dean was silent for a moment, stunned.  
  
"What?" he finally said.  
  
"I found it for you, Dean," Cas told him. He squared his shoulders and met Dean's eyes again, steeling himself for the human's reaction. "A pearl is the traditional betrothal gift of my people. The size and color indicate the giver's... regard. The larger, rarer, and more perfect the pearl, the more serious the suit." He had swum the other oceans in search of the perfect gift, occasionally grabbing onto a friendly whale's fin when his own tail was too tired.  
  
"Betrothal?" Dean's voice was shaky, shock dominant. Cas gently touched Dean's face and the human leaned into the touch before swallowing thickly around the lump in his throat. "Cas... are you sure?"  
  
'Are you sure you want me?' was the unvoiced question. It was one Dean would never let himself ask out loud, even though Castiel had seen it lurking in the depths of his eyes.  
  
"I am over thirty Seasons old," Cas said. Season came around once a year by human standards, the time when most of the fish paired up and produced offspring. "I have known you for twenty of them and been with you like this-" He squeezed Dean's hand. "-for three. I sought a pearl worthy of you for months before I found this and I still don't think it's enough to represent how I feel. I am certain."  
  
"Sap," Dean choked out. His fingers tightened around the pearl and he firmed the line of his jaw. He offered the pearl back to the merman. "Cas, we can't."  
  
Cas felt as if an unexpected current had grabbed him by the tail and yanked him miles off course.  
  
"Why can't we?" he demanded, pulling his hand away from Dean's face but refusing to take the gem. The water swirled angrily around his arm. His tail thrashed, stirring up more water.  
  
"Look, I want this as much as you do-" Dean began.  
  
"Then why are you rejecting me?" Castiel demanded. Dean scowled.  
  
"Because it's not as easy as just saying 'yes' and getting a 'happily ever after', all right?" he snapped. "Cas... I want this. A lot. But mermaids take one mate, and only one mate, for their whole life, right?"  
  
Confused by the sudden shift in topic, Cas nodded.  
  
"This-" Dean indicated himself, from the fins on his feet to the air tank strapped to his back. "-isn't going to work for that long. Hell, as it is I get to spend a half hour with you every other day if I'm not busy."  
  
"Are you getting tired of meeting with me?" Cas asked quietly, chest tight and voice strained.   
Dean shook his head vehemently, sending shockwaves through the water.  
  
"I'd be down here every day for hours if I could, you know that," he said. "But I can't. Not even your mojo can swing that. And eventually, you're going to resent getting saddled with a mate that can't even... fuck, Cas, we can't even make out properly." They had shared kisses before, but they were generally rushed, brief things before Dean hurried to get his mask back on. They had tried, once, to get to the surface to kiss for longer, but Cas had gotten ten feet to the top and gotten so dizzy he'd needed to descend back to where the water was heavier. "You're going to want more than that and I can't do anything for you." Merman biology and human biology was incompatible, as Cas and Dean had discovered to their dismay. While Cas could use his hands or mouth to bring Dean off, Dean could only use his hand to bring Cas any sort of pleasure. It gave neither of them the closeness they craved: the feeling of being wrapped up in one another, closer than skin. They couldn't even lose themselves properly in the sensations, not when drifting too far up or down would cause one of them to get sick and Dean's thin, plastic mask was the only thing sealing air against his nose and mouth. Their few, fumbling attempts at sex had been carefully planned out.  
  
Still, if Dean accepted him, then the ocean would no longer be an obstacle.  
  
"I only want you," Cas said. "If you are rejecting me, then do not do it because you think I'm going to want someone else if you can't satisfy me. Do it because you don't want to be with me anymore."  
  
"I want you," Dean said through gritted teeth. "But that doesn't change anything. We can't-"  
  
"Then why did we begin this at all?" Cas snarled, fins fanning out and making him look larger. He resisted the urge to yank his hand away from Dean, knowing his 'mojo' was the only thing allowing them to communicate. He couldn't break the connection and risk saltwater filling up Dean's mask or the human's words becoming garbled by the weight of the water above them. "Why didn't you break it off as soon as you realized that a merman and a human could never truly join, if that is so important to you?"   
  
"Because I'm a selfish bastard, all right?" Dean shot back. "And I want to fuck you so badly it hurts, but that's not what's most important to me. I've been with you for three years now, Cas. Three years. I wouldn't do that just for sex." Dean was crude by nature, but his voice was soft and reverent on the word 'fuck' and his eyes were warm and full of longing.  
  
"I know," Cas replied, anger draining out of him. He curled Dean's fingers around the pearl and shoved it gently back at him. "That's why, if you accept my gift, I have decided to Ascend."  
Dean inhaled sharply, his grip slackening on Castiel's hand and the pearl.  
  
"You'd become human?" he asked numbly.  
  
"If you'll have me," Cas said softly. "Gabriel has already agreed to cast the spell. I just need to ask and then, once my tail fully dries and I've washed off the salt of the sea, I'll no longer be a merman."  
  
"But- Cas... you can't do that. Not for me," Dean said, tripping over his words. "This is your family down here, dude. What about your brothers? Your sister?"  
  
"I have said my goodbyes, Dean," Cas said. "They've given me their blessing. This isn't a permanent farewell; you'll teach me how to dive like you do and we can visit them." Cas touched Dean's face again and moved in closer. They couldn't kiss, not with the mask in the way, but getting closer was a comfort. "Please."  
  
Dean was silent for a moment. Castiel hardly dared to breathe, listening to the sound of the currents and Dean's slow, deliberate inhalations.  
  
“Cas,” Dean finally said. “It’s not going to be easy. Nothing’s ever easy, so just stop and think-“  
  
“Do you think I’m a child, Dean?” Cas asked, bristling. “I’ve thought of this for over a Season now, even before I began my search for your gift.”  
  
"Have you really?" Dean snapped. "Up there, you're going to need money, identification, a job... it's completely different from how things are down here."  
  
"I know. I've learned what I can from other families with relatives that have Ascended," Cas said. "I know it is nothing like life down here, but you can teach me how to be human." There was a beat of silence. "Unless it's too much to ask."  
  
"Too much?" Dean snorted a laugh. "Damnit, Cas, you're giving up everything to be with me. What kind of an asshole would I be if I didn't show you the ropes? I'll teach you." He paused, apparently surprised by his own words.  
  
Castiel felt a warmth spread throughout his body, warmth and light and hope. His flicked his tail more quickly, trying to keep himself from getting too excited.  
  
"Do you really mean that?" he asked. Dean swallowed heavily and nodded.  
  
"Yes. I'll teach you how to walk, how to dive, I'll teach you anything you want," he said. "But only if you're sure. If you Ascend, there's no going back."  
  
"I am sure," Cas said simply. His heart pounded. "Do you accept my gift, Dean?" It wasn't just the pearl Cas was referring to, but himself as well. He would be completely at Dean's mercy, but the thought caused him no panic. Dean's hands were strong and capable.  
  
"Yes." Dean squeezed Castiel's hand. He knew exactly what he was accepting. "Fuck yes."  
Cas felt the tension drain out of his body, only to be replaced with an exulted kind of terror. The desire he'd been harboring for over a year now would become reality.  
  
"Breathe in deeply," Cas commanded, moving his hand to the seam of Dean's mask. Dean took in a big lungful of air and then Cas slipped the mask off his mouth. Bubbles burst forth from the regulator. Cas knocked it aside before pressing his lips hungrily to Dean's, reveling in the contact and groaning quietly at the thought of soon being able to do more than just kiss. Dean kissed back, the salty tang of seawater heavy on his tongue, but all too soon they had to part.   
Dean quickly reeled his mask back in, then fixed it in place and flushed the water from inside.   
His chest heaved as he gulped for air.  
  
"Can't wait until we can do that all day if we want," Dean said. Cas felt his skin grow hot, want collecting in him as he imagined a day spent in bed with Dean, kissing lazily and making love leisurely because they had the advantage of time.  
  
Dean checked his waterproof watch and cursed quietly.  
  
"I'm running low on air in this tank. I need to surface." He hesitated, nervous but excited. "When are you going to Ascend?"  
  
Castiel considered for a moment, fins fluttering more rapidly than could be blamed on he current.  
  
"I need to pack my things," he said. He had very little and had considered packing before swimming out, but he hadn't wanted to presume. "If you'll wait for me at the surface-"  
  
There was a flare of magic, more powerful than Castiel's own, and then another voice joined them.  
  
"Actually, bro, you're all set."  
  
Dean and Cas turned to face the sound. Gabriel swam towards them, a large bag woven from seaweed in his hands. His tail was long and mostly white, though there were thin reddish-orange and deep brown stripes along the length of it. His fins were narrow and spread out along his back and his forearms like fans, waving gently in the current. Gabriel smirked and pulled up alongside the couple.  
  
"I grabbed your stuff for you," he said to Cas, offering him the bag. Cas took it in one hand, still holding onto Dean with the other. The bag was unexpectedly heavy and Castiel frowned.  
  
"What else did you put in here?" he asked, suspicious and curious in equal measure. His few possessions combined wouldn't weigh this much and Gabriel was well-known in the village for pulling pranks. Gabriel waved a dismissive hand.  
  
"A few going-away presents," he said. "Nothing bad, I promise. They're from everyone in the family."  
  
"Right," Dean said sarcastically, eyeing the bad with undisguised wariness. He had good reason. After Dean and Cas had started their courtship (which Dean referred to as 'dating'), Cas had brought his siblings to meet Dean. Gabriel had shoved an eel down Dean's swimming trunks. Dean's frantic dance to get the eel out had ended with the shorts halfway down his legs and everyone present getting an eyeful. "What's your definition of 'bad', again?"  
  
"Anything that hurts my family," Gabriel replied cheerfully, though his eyes had turned serious. Even his hair, long and floating around his head like a halo, wasn't comical enough to cover up the solemnity in his gaze. "So if you don't want to get turned into seafoam, I suggest not breaking Cassie's heart."  
  
"Gabriel-" Cas started, torn between being grateful for the bag and bristling at the threat to Dean. Cas could protect himself.  
  
"No, it's OK. I get it," Dean said. He didn't say anything else, but he did grip Castiel's hand tighter and paddled a bit closer. Gabriel's eyes flicked to their joined hands and he smiled.  
  
"You're not bad, kid," Gabriel said. "Knew I liked you for a reason." Gabriel brought his hands together in a slow clap, expression playful once more. "So, I'll just cast the spell and you two angelfish can be on your way."  
  
"Thank you," Cas said. He glanced at the bag again and frowned. "How did you know to pack my things?"  
  
"The only one who was in doubt that Dean-o here would say 'yes' was you, Cas," Gabriel said. "I had to threaten him if he broke your heart, though, or else I'd lose my big-brother-club card. Those are a nightmare to replace." He raised an eyebrow. "Unless you'd prefer Lucifer to do the obligatory 'they'll never find the body'?"  
  
"No, that's fine," Cas and Dean said in unison. Depending on what kind of mood Lucifer was in, especially if he had been fighting with Michael, Lucifer might try to preemptively follow through on the threat.  
  
"That's what I thought," Gabriel said, pleased. He looked at Cas. "Ready to go?"  
  
Castiel felt a sudden pang of loss in his chest. Gabriel was smiling, but the expression didn't reach his eyes. Gabriel would miss him, just as Cas would miss his family. Cas would miss his home, his tail, his whole life down here. He'd miss being able to slice through the water quickly and easily. He'd miss waking up in his grotto and swimming out to see everyone he knew.  
  
Dean squeezed his hand, subtly so that Gabriel wouldn't notice. Cas squeezed back.  
  
The losses he'd suffer were dull aches, pains he had already accepted as the price for being with Dean. His future with the human was bright and big in his mind, like the light that filtered down from the top layers of the ocean. It helped that he wouldn't need to say goodbye to everything he knew permanently. He would never see the home he had grown up in again, since it was too far beneath the ocean's surface for a human to reach. But he'd learn how to work the rubber fins Dean wore and they would replace his tail. His siblings would visit him here, just as he had always visited Dean, and they would bring him stories of home. And he would make a new home on the surface. With Dean.  
  
"Yes, I'm ready," he said. Gabriel snapped his fingers, eyes glowing briefly white, and though the sound didn't travel at all underwater, the magic did. The water around Castiel's tail began to churn, first sliding over and then slipping under the dark scales. Cas breathed in sharply, clutching at the seaweed bag and Dean's hand as the water slid through his skin and the muscles of his tail, splitting it in two inside the barrier of his scales. The water burned like hot acid, and then it wasn't just burning his tail. Cas's next breath of ocean water burned his lungs and spread out through his chest, boiling every one of his internal organs until they were just lumps of flesh to be molded anew. His fins burned, the spines keeping them upright white-hot.  
  
He'd been prepared for pain, but he hadn't expected it to hurt this badly.  
  
"Cas?" Dean asked as Cas doubled over. He shoved the pearl in the pocket of his trunks and grabbed Castiel's shoulder. Cas's expression was pained and tight, his breathing heavy, and Dean shot a venomous glare at Gabriel. The other merman was watching Cas with sympathy, fingers twitching as though he wanted to cast another spell. "What the hell did you do"  
  
"He's becoming an entirely different species, genius. Did you think it would be all coral reefs and clownfish?" Gabriel shot back.  
  
Then, just as suddenly as the pain had come, it subsided. Cas could still feel the water draining out, leaving behind a strange emptiness. His insides felt like clay, his tail felt too large, his fins felt like the slightest current could crumble them into nothing. The pain hovered just out of reach, not present but threatening to return.  
  
"Thank you," he told Gabriel weakly, clinging a little tighter to Dean. He felt dizzy and didn't trust himself to swim straight. Dean tugged one of Castiel's arms over his shoulders and wrapped an arm around the merman's waist, supporting him.  
  
"Take care, little brother," Gabriel said. He looked at Dean. "Dry him off quickly and dump sweet water over him; it'll make the change permanent. You have some on your boat, right?"  
  
"Yeah," Dean said, eyes glued to Castiel. There was a small tank of fresh water the Winchesters used whenever they went out for longer fishing trips. The tank would still be full from their last trip, if a bit stale. Dean shot a quick glance to Gabriel. "Being in the ocean won't hurt him after, will it?"  
  
Gabriel snorted.  
  
"No. It's just the initial rearrangement of all his internal organs and the loss of his tail."   
He snapped again, eyes once more flashing white, and then waved impatiently. Dean felt the water around him begin to drop in pressure, slowly enough that his body had no trouble adjusting. He wouldn't need to worry about getting the bends, even if he swam directly upwards without safety stops. "Now go, already. Cassie can answer your questions once he's a bona-fide two-legger."  
  
"I'll be fine, Dean," Cas said, more reassuringly. Dean nodded, brow creased with worry he wouldn't let himself voice.  
  
"Thanks, Gabe," he said gruffly. He firmed his grip on Castiel and then they ascended together, Dean's powerful kicks and Castiel's tail propelling them quickly towards the surface.  
  
Gabriel watched them go, a thin smile on his face.  
  
"Good luck, baby bro," he said. He turned and swam for home just as Castiel broke the surface and inhaled his first of many breaths of ocean air.  
  



End file.
